1. Field of the Invention
The present invention relates to a catheter to be used for diagnosis and medical treatment and also to a guide wire to keep the catheter approximately straight. More particularly, the present invention relates to a catheter and a catheter guide wire which have improved resistance to corrosion by body fluids and drugs. The catheter has such an entirely new structure that the forward end thereof is provided with a heating part which permits the accurate temperature control of the medicine to be injected hot.
2. Description of the Prior Art
Much attention is now focused on the new method of diagnosis and medical treatment which involves the insertion of a tubular catheter into the heart, lung, stomach, or blood vessel for the extraction of body fluids or blood or for the infusion of blood or medicine. The catheter for this purpose has an L-shaped tip and is flexible so that it can be inserted into complicatedly bent blood vessels. To facilitate insertion into the body, the catheter is kept approximately straight by the aid of a guide wire inserted into it. This guide wire should have the following characteristic properties.
Sufficient flexibility to permit the catheter to bend easily along the blood vessels. PA1 Sufficient strength to keep the tip of the catheter approximately straight. PA1 Small outside diameter to permit its insertion into the thin catheter. PA1 Good resistance to corrosion by body fluids and blood. PA1 Small outside diameter and large inside diameter. PA1 Good flexibility. PA1 Good buckling resistance (which prevents the catheter from being collapsed when it is bent). PA1 Ability to transmit torque (for manipulation) to its tip.
The conventional guide wire which meets these requirements is composed of a stainless steel core wire and two layers of windings of extremely thin stainless steel wire (about 30 .mu.m in dia.) on the core wire, with the inner windings being oblique to the axis of the core wire and the outer windings crossing the inner windings.
What is required of the above-mentioned catheter for diagnosis and medical treatment are:
The conventional catheter to meet these requirements is made from a tube of fluoroplastic (such as Teflon).
The above-mentioned catheter has recently found a new use for the remedy of obstructive jaundice induced by liver cancer. In other words, the catheter is used to inject blood or medicine (such as anticancer drug) hot directly into the affected part. The conventional method involves the heating of medicine by a warmer coil and the injection of the heated medicine through the catheter.
For the effective diagnosis and medical treatment, it is necessary that the catheter be brought as close to the affected part as possible. This requires the catheter to have a smaller outside diameter and the guide wire to have a smaller diameter accordingly. A conceivable way to meet this requirement is by further reduction in the diameter of the stainless steel wire. Mere reduction in diameter, however, results in insufficient strength, making it difficult for the guide wire to keep the catheter straight, which leads to the inconvenient manipulation of the catheter. There is a limit to reducing the diameter of the stainless steel wire.
One possible way of reducing the outside diameter of the conventional catheter is by the reduction of the wall thickness of the inserting part, because it is necessary to secure a certain inside diameter necessary for blood extraction or medicine injection. A problem associated with reducing the wall thickness is that the catheter is liable to collapse and to become poor in torque transmission ability. This is another factor that limits the reduction of the diameter.
It is expected that the reduction in diameter of the guide wire and catheter will be achieved with the low carbon duplex structure steel wire which had previously been proposed by the present inventors. It is produced from a wire rod, 3.0-6.0 mm in diameter, composed of C: 0.01-0.50%, Si: 3.0% or less, Mn: 5.0% or less, with the remainder being Fe and inevitable impurities (by weight), by the steps of primary heat treatment, primary cold drawing, secondary heat treatment, and secondary cold drawing. The thus produced steel wire has a diameter smaller than 30 .mu.m and a tensile strength higher than 300 kgf/mm.sup.2. In other words, it is stronger and tougher than stainless steel wire for the same diameter. Therefore, if the low carbon duplex structure steel wire is used as a reinforcement for the guide wire and catheter, it would be possible to reduce the diameter while meeting the above-mentioned requirements.
Unfortunately, the low carbon duplex structure steel wire has a disadvantage that it immediately rusts upon direct contact with body fluids, medicine, or air because it is extremely thin. Therefore, it should be given corrosion resistance.
According to the conventional practice it is necessary to heat medicine or blood using a warmer coil before it is injected hot through a catheter. The heated medicine or blood decreases in temperature when it reaches the affected part and the actual temperature is not known. In other words, the method for injecting blood or medicine hot through the conventional catheter poses a problem associated with inaccurate temperature control.